The present invention relates to a light fixture for projection devices, especially for microfilm viewing and enlarging machines.
A standard light fixture for projection devices includes an electric bulb serving as a light source, a socket for holding and providing an electrical connection of the light bulb, a concave mirror serving as a reflector, and an optical condenser system, whereby the bulb socket and the concave mirror are combined into a first constructional unit, hereinafter referred to as the "lamp unit," that is detachably connected with a second constructional unit containing the optical condenser system. The bulb is movable for the purpose of centering its filament coil in relation to the concave mirror, and the condenser unit is fixedly mounted in a projection device, while the lamp unit is merely supported by the condenser unit.
In such a light fixture, in order to achieve good light output, it is generally required that the bulb be movable in relation to the concave mirror and the condenser lens system, so that the filament coil of the lamp and a mirrior image of the filament coil produced by the concave mirror can be moved into a predetermined position relative to one another, and so that they can be reproduced together by the condenser lens approximately on the axis of the light fixture at a point located inside the projection lens of a projection device in which the light fixture is being used. However, known embodiments of such light fixtures use relatively expensive means for setting up the socket for the light bulb, whereby in many cases, the concave mirror and the optical condenser system are mounted in such a manner that they are stationary and cannot be moved relative to one another. Furthermore, the proper adjustment of the bulb for centering its filament coil is difficult and complicated for non-experts to check. And, it is either entirely impossible or possible only in a relatively complicated manner to adjust the bulb in such known light fixtures to projection lenses with varying focal lengths. Thus in practice it often occurs that the light fixture is operated without optimal adjustment, and consequently the light output achieved is imperfect or entirely inadequate.